(a) As used in this Code section, the term:

(1) "Full-time service" means any service in a covered position during which such member was generally prohibited from the practice of law by virtue of holding such position.

(2) "Part-time service" means any service in a covered position during which such member was not generally prohibited from the practice of law by virtue of holding such position.

(b) Any member who, on the effective date of his or her retirement, was serving in a part-time position shall be entitled to use all of his or her prior service credit for purposes of vesting for benefits and for the calculation of benefits.

(c) Any member who on the effective date of his or her retirement was serving in a full-time position shall not be entitled to use any prior part-time service for vesting for benefits and shall be entitled to use such prior service for the calculation of benefits on the basis of one month of credit for each three months of prior part-time service.

(d) Notwithstanding any provision of subsection (b) or (c) of this Code section to the contrary, any member who became a member pursuant to Code Section 47-23-40 shall be entitled to calculate his or her service as provided in the predecessor retirement system of which he or she was a member.